It's indeed robo-call, rings. you answer, slight pause <always, never the usual "Hello" from a real person>, then their message comes on <usually a real operator>...suggest answering, then hang up immediately as soon as you recognize the pause since it's tough to delete. This way you don’t have to listen to it.
Or another way, is to introduce yourself as Mr. ___ from the ___County Sheriff’s department, and tell them they have just called a murder scene, that there’s no need to identify themselves since you already know who they are and where they are calling from...and unless they have something to say that might relate to your investigation, suggest they hang up and don’t call back unless they remember something that may help in the investigation. As we now track all calls to this number, you will hear back from one of our investigators in the future.
Side-note: I have to admit that I once used robo-call (telemarketing), but that was back in 1977. These self-declared entrepreneurs are no different than I was 40 years ago. The difference was we were all looking for ways to survive the economies of the times, but overtime we should realize the difference between being a relentless nuisance and bloodsucker VERSUS a modern eco-friendly company actually engaging in real communication with people.
No one should ever give any information of any kind to <unknown> solicitors like these who employ out-dated sick marketing efforts.
I'll make a copy of all this and send it to the FTC so there's a federal record of this number and person since he / she can also be identified.